Enrichment experiments were performed in the Ross Sea to test the hypothesis that iron deficiency is responsible for the phytoplankton's failure to use up the luxuriant major nutrient supplies found in these and all other offshore Antarctic ocean waters. The results suggest that Fe deficiency is the primary reason that the present-day southern ocean biological pump is shut off. In contrast, iron was 50 times more abundant during the last glacial maximum; greater Fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric CO 2. These results also imply that large-scale southern ocean Fe fertilization is feasible, at least in terms of the total amounts of Fe required; i.e., 100 000 to 500 000 tons yr -1., Cited By (since 1996):277, , , Downloaded from: http://onlinelibrary.wiley.com/doi/10.1029/GB004i001p00005/pdf (9 June 2014).

Excess major nutrients occur in offshore areas ranging from the tropical equatorial Pacific to the polar Antarctic. In spite of the great ecological differences in these environments, they share a common trait: iron deficiency. All of these areas are far from Fe-rich terrestrial sources and atmospheric dust loads in these regions are amongst the lowest in the world. Experiments were performed in three nutrient-rich areas: The Gulf of Alaska, the Ross Sea, and the equatorial Pacific. In general, populations without added Fe doubled at rates 11-40% of the expected maxima at various temperatures. The addition of nanomole quantities of Fe increased these doubling rates by factors of 2-3. In spite of the lack of Fe, tightly coupled phytoplankton/zooplankton communities seem to inhabit these major nutrient-rich areas. -from Authors, Cited By (since 1996):341, Oceanography, , , Downloaded from: aslo.org/lo/toc/vol_36/issue_8/1793.pdf (16 June 2014).

WE are testing the hypothesis that Antarctic phytoplankton suffer from iron deficiency 1-3 which prevents them from blooming and using up the luxuriant supplies of major nutrients found in vast areas of the southern ocean. Here we report that highly productive 4 (∼3 g Cm -2 day -1), neritic Gerlache Strait waters have an abundance of Fe (7.4 nmol kg -1) which facilitates phytoplankton blooming and major nutrient removal, while in low-productivity 4 (∼0.1 g Cm -2 day -1), offshore Drake Passage waters, the dissolved Fe levels are so low (0.16 nmol kg -1) that the phytoplankton are able to use less than 10% of the major nutrients available to them. The verification of present-day Fe deficiency is of interest as iron-stimulated phytoplankton growth may have contributed to the drawing down of atmospheric CO 2 during glacial maxima 2,3; it is also important because oceanic iron fertilization aimed at the enhancement of phytoplankton production may turn out to be the most feasible method of stimulating the active removal of greenhouse gas CO 2 from the atmosphere, if the need arises (J.H.M., manuscript in preparation)., Cited By (since 1996):449, CODEN: NATUA, ,